1. Field of the Invention
The present invention is concerned with novel compounds having alkenyl or alkenyloxy groups, their manufacture, liquid crystalline mixtures which contain these compounds as well as the use of these compounds and mixtures for electro-optical purposes.
2. Description
Liquid crystals have recently gained considerable importance as dielectrics in indicating devices, since the optical properties of such substances can be influenced by an applied voltage. Electro-optical devices based on liquid crystals are well known to the person skilled in the art and can be based on various effects such as, for example, the dynamic scattering, the deformation of aligned phases (DAP cell) the Schadt-Helfrich effect (twisted-nematic cell), the guest/host effect (guest/host cell) or a cholesteric-nematic phase transition (phase change cell).
The liquid crystals which are used must have a good stability towards heat, moisture, air, electromagnetic radiation, electrical fields and the like. Further, they should be colourless, should have short response times and low viscosity, should give a good contrast and should have a nematic or cholesteric mesophase in the entire temperature range in which the liquid crystal cell is to be operated. Since liquid crystals are usually used as mixtures, it is, moreover, important that the components have a good miscibility with one another and at the same time form a nematic or cholesteric mesophase. Other properties such as, for example, the electrical conductivity, the threshold potential, the multiplexibility and the dielectric anisotropy must fulfil different conditions depending on the type of cell which is used.